Do NOT tip your hand here, this is critical. Theres a lot more she could do before any legal steps are in place that could cause even more damage.
Take the first step, consult an attorney. Get his advice on how to proceed to protect yourself and your childrens future. He will best know how to proceed.
Your job right now...........KEEP QUIET, KEEP TO YOURSELF, TELL NO ONE. Act as normal as you can, and don't let on that you know anything until you can get the advice of your attorney.
Don't be vindictive right now, it will not help a thing. Please take care of yourself and your kids right now, and let that be your focus until things get reviewed.